Pressure transfer device



Feb. 20, 1945. A 2,369,707

PRESSURE TRANSFER D-EVICE Filed April 6, 1942 2 Sheets-Sheet l SUPERCNARQER.

INVENTOR. Alba-1" E gen-2.14...

, Patented Feb. 20, 1945 PRESSURE TRAN SFER DEVICE Albert E. Baak, Minneapolis, Minn, asslgnor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn. a corporation of Delaware Application April 6, 1942, Serial No. 437,862

ioclaims. (Cl. 73 395) Thi invention relates to a remote pressure transmission system that provides for the increased accuracy and sensitivity in operation by fluid means of various types of aircraft indicating and control devices. In particular, the system of my invention relates to the operation of such instruments from a capillary fluid line that may be of considerable length, and in which the fluid is substantially unaffected by wide variations of pressure and temperature to which it may be sub- Jected, in cooperation with my novel fluid pressure transmission cell. Phe pressure transfer cell of my invention serves as a combination condition responsive device and hydraulic motor means for controlling the instrument actuating fluid.

Prior to my invention the widespread practice for the operation of. gasoline and oil pressure in-' strumentslocated in the control rooms of aircraft was by direct connection of the instruments with the gasoline and oil lines. The gasoline. and

oil lines were of relatively small diameter with the fluid therein subject to more or less variation in Viscosity and other characteristics when subjected to wide changes in temperature and pressure conditions of the line. It is apparent that by this system it was necessary to run lines conveying inflammable gasolin and oil another fluids to the control room and thus create a potential fire hazard, and also thatfrequent checking and a novel pressure transfer cellemploying a dia-' phragm therein for the direct transmission of gasoline, oil or other fluid pressure from the diaphragm through an extremely sensitive fluid which I enclose in a capillary hydraulic. line to afford rapid, accurate and sensitive operation of an instrument, since the capillary line may be of considerable length and exposed to widely varying external conditions.

It is another object of my invention to provide important safety features in the operation of aircraft gage and control devices by making possible their separation from and, if desired, remote location with respect to lines conveying the gasoline, oil or other'inflammable fluid.. In accordance with my invention the pressure transfer cell together with the gasoline or oil line are located in one zone and separated by a fire resistant wall from the. gage or control devices which are located in a second zone. A further safety feature of the system of my invention is the provision of a diaphragm means in the pressure transfer cell for preventing the entrance of the gasoline, oil, or other fluid to the hydraulic operating line and to the gage and control devices operated thereby. even upon failure of operation of the hydraulic line or of the devices. For example,

'the hydraulic line as employed with aircraft; may be of the considerable length required to extend cleaning of the instruments and lines was neces-f sarily required, due to their not forming a hy-v draulic system closed against entry of extraneous matt er. I

It is an object of my invention to provide a I safety system in which my novel pressure transfer cell "is employed as a condition responsive device in close association .with a relatively short gasoline-or oil fluid pressure line of relatively large diameter. This is advantageous because gasoline, oil or other fluid in a line of relatively short length is not substantially afiected by external temperature-conditions and also because [the linemay be of such relatively large diameter Yes to require little any cleaning in order to insure proper operation of the system. The cell of my invention cooperates with a line containing.

a separate instrument actuating fluid and provides for the automatic compensation .of'the system for external variations in temperature, for separating the instrument actuating fluid from from the engine through a zone associated with a portion of the wing in which the engine may be located and to devices located on a panel in the control room. The devices and the hydraulic line in particular may be subjected to widely varying vibration and temperature conditions. However, upon breakage or Iailure'of the hydraulic line or devices my system, unlike previous systems in widespread use, will operate to prevent the gasoline, oil, or other fluid to which the pressure transfer cell-responds from escaping tocreate a potential fire hazard in various parts of the aircraft.

A furthelr'object of my invention is the provi-.

- sion of a new and novel pressure transfer cell the inflammable gasoline and oil, and also for transmitting pressure of the-gasoline, oil, or other fluid to the actuating fluid for the operation of Q the instrument.

Another object of my invention is to provide unit. The cell unit provides for two fluid chambers separated bya diaphragm and to a first of thetwo chambers a relatively large line maybe connected for the admission thereto ofa fluid of variable pressure. This fluid may consist of gaso line or oil which directly actuates the diaphragm in. accordance with variation in the pressure of the fluid; or an intermediary fluid may be employed which may be varied in response to temperature or other conditions. The cell unit is employed as a motor for the hydraulic transmission of pressure variations in the first chamber to a fluid in the second chamber thereof. The second chamber has both means for initially admitting a fluid thereto and means affording a connection between the cell and the line or reservoir for the normal operation of the instrument or instruments connected to the line or reservoir. The volume of the fluid in the second chamber and the size of the diaphragm are such as to automatically compensate for external changes in temperature and pressure throughout the system. In the operation of the system of my invention,

the actuating fluid in the second chamber and in.

the line associated therewith is preferably adjusted initially to a pressure value of one atmosphere.

A still further object of the invention is to provide means in the pressure transfer cell to restrict and limit any rapid and large surges in the flow of the fluid when the system is in actual operation. The preventio of large and rapid surges in fluid flow serves, for example, to prevent injury to the diaphragrn should a leak or break in the system occur which might otherwise result in the application of a suddenly applied force of a magnitude sufficient to injure the diaphragm.

One object of my invention is the provision of a system in which fluid operated instruments, including gages and control devices, may be accurately and rapidly actuated in response to re motely located condition responsive means and in which the interval between inspections of the system required for checking, overhauling, cleaning and refilling of the elements is greatly lengthened. A further object of my invention is the provision of a method for the rapid, accurate and advantageous checking, cleaning and refilling of a hydraulic system, compared to the methods required in connection with other known systems.

A particular object of my invention is the provision of a method for rapidly checking, cleaning and refilling the line and transfer cell elements of my system by making possible the introduction of the hydraulic fluid to the pressure transfer cell under high pressure for distribution throughout the system and by providing for the draining of the fluid at high pressures from the system until the flow of draining fluid is free of entrapped air to thus indicate that the remaining fluid is in condition for the proper operation of the system, when the supply of fluid under pressure may be discontinued, permitting the fluid in the system to attain atmospheric pressure conditions.

A more detailed object of my invention is the provision in one chamber of my pressure transfer cell unit of a diaphragm backing plate which is movable therein and employed to support the diaphragm without deflection by fluid pressure when the hydraulic fluid is initially introduced to the-cell and system under relatively high pressures, the other chamber being unaffected, and I Figure 2 is a diagrammatic view partly in section of my system during a portion of the checking and filling operations, and

Figure 3 is a diagrammatic view partly in section of a modification of the pressure transfer cell unit employed in my system.

The system is first described below when assembled for normal operation as illustrated in Figure 1. The engine fuel, or oil line, In is threadedly connected to a manually operated valve member II and this member is threadedly attached to-the pressure transfer cell unit generally indicated at I2 by a direct connection |3 with the fluid pressure chamber M. The pressure chamber I4 is deflned by a diaphragm l5 and the pressure transfer cell casing member IS.

A diaphragm backing plate member 20 is supported for movement in the chamber M. A locking screw member 2| is supported in the housing l6 and the head portion is secured in a flanged recess formed in the follower member 22 upon which is supported the diaphragm backing plate 20. A gasket 23 is mounted on the screw member 2| and secured to the flanged follower member 22. In the normal operation of the system the diaphragm backing plate 2.0 is in the diaphragm non-supporting position to which it is locked by the screw member 2| and the lock nut 24. The diaphragm backing member 2|) is employed in a manner which is described befluid, line at 33 and also to a supercharger 'or other source of fluid pressure by a threaded connection with the line 34. The fluid pressure actuated switches may be employed to control separate signal and control devices and are pref erably of the type disclosed in my copending application Serial No. 437,863, flied April 6, 1942. However, in the event that it is not desired to employ pressure'switches 30 and 32, these members may be omitted and plug members may be substituted therefor in the transfer cell and in the line.

The cell diaphragm Hi and the cell casing member 40 defines a second chamber 4|. Chamber I4 is somewhat larger than chamber 4| where they respectively contact diaphragm l5, so that a ledge 48 is formed by a portion of the wall of chamber 4|. On actuation of locking'screw 2| the backing plate 20 seats firmly against and is aligned 'with the ledge 48 through diaphragm I5, and accordingly diaphragm I5 has an unyielding support over its whole area. The casing member 40 has a series of passages 42 formed therein to provide for communication between a I threaded Passage member 43 formed in the casing member 4|] and the cell chamber 4 l. A check valve consisting of an orifice plate and valve seat member 44, a ball valve'member 45, and a spring valve biasing member 46 is contained in the passageway 43. ,The check valve serves to permit a flow of fluid through the passage 43 to the chamber 4| and to prevent the escape of fluid therefrom, as hereinafter set forth, but in r the. normal operation of the system a threaded plug member 41 is mounted in the passageway 4:. A series of orifices so areformed in the casing 40 and these orifices provide for communication between the threaded casing passageway 5| and the chamber 4| V The pressure transfer cell unit is closely associated with the aircraft engine or other fluid source 7 to which the line I II extends and this line I is the fire wall 55 and with the threaded passageway of the pressure transfer cell.

The capillary line 54, may be of considerable length, such for example as required to extend from wing mounted aircraft motors and through the wings of the a rcraft to the control cabin for cooperation with a panel mounted indicating or' control instrument 10. The line 54 is' connected at one end by a plug 65 having the mounting The pressure transfer cell may be phragm, The elastic diaphragm is of sufficient size and strength to continue in operation for the purpose of preventing the ignitable gasoline, oil

or otherfluid from gaining access to the chamber 4| and the associated portions of the system.

The novel method of cleaning, checkin and filling the elements of my system is illustrated in Figure 2 and similar reference characters have been applied to parts of the system corresponding to similar parts employed in the normal operation thereofas illustrated in Figure 1. Also, in

Figure 2, the switch devices and 32 have been members 66 and 61 associated therewith to a v main plug member 68 for cooperation with a passageway 69 extending therethrough, The

main plug member 68 has associated therewith a 1 second threaded passageway 12 which also communicates with the passageway 69 andva branch plug member 13 is mounted in this threaded branch passageway. The main plug is associ ated directly with the instrument 10 and the plug passageway 69 cooperates with a passage-' way 14 in the instrument.

' A fluid is employed in the chamber 4| of the pressure transfer cell and in .the capillary line 54 for theoperation of the instrument 10 which will accurately and rapidly actuate the instrument in accordance with the varying pressure transmitted by diaphragm I5 of the pressure transfer cell. This fluid is preferably of a type branch plug 13 illustrated in Figure 1 of' the that is substantially unaffected by the relatively great external variations in temperature to which the elements of my system may be subjected, that is non-inflammable, that will not .corrode the line and that will not cause'clogging of the system throughout the wide range of temperature to which it is subjected. Fluids having desired operating characteristics and which I prefer for use in my system are Stanisol or Stoddard Solvent.

In the operation of my system the pressure from the fluid fuel or oil admitted to the cham-' ber I4 of the pressure transfer cell is transmitted by the diaphragm I5 which is of relatively. thin and highly elastic material to the hydraulic fluid'in the chamber 4| and the capillary line 84 for the sensitive and accurate operation of the instrument l0. The orifices 50 of the pressuretransfer cell are sufliciently numerous to cause no appreciable effect on the normal flow of fluid between the pressure transfer cell and the capillary line 64. Should a failure occur in the operation of my-system of a type which, for example, might involve a leak or break in the capillary line the hydraulic fluid would be permitted to escape from the chamber of the pressure transfer cell. The orifices 50, however. serve to prevent the escape of fluid in a rapid and large surging movement that might damage the diaomitted from the system and a plug member inserted in the pressure transfer cell passageway .29'has been substituted for the switch 30.

"In filling the system with the hydraulic fluid I employ a manually operated air pump and fluid reservoir member 8|. The member 8| consists of a chamber 82 containing fluid 83 and a cover member 84 The manually operated pump con-. sists of the cylinder 85 containing the plunger which is operated by-the rod and handle 86. The

cylinder has a pipe eirtension member 81 for ad- 1 mitting air pressure from the pump to the upper surface of the fluid in the reservoir 82. I Upon operation of the pump a pressure is accordingly exerted upon the upper surface of the fluid and this serves to force the fluid through the outlet pipe 88 which extends to the lower portion of the reservoir. A gage member 90 is provided on the cover member 84 for indicating the pressure applied to the fluid and a hand operated valve 9| is associated with the fluid outlet pipe 88 to control the flow therefrom. The valve member is connected by a tube 92 and the associated members 93 and 94 to the passageway 41 of the pressure transfer cell.

A fluid drain container S'I-and a drain pipe 98 are associated with a plug99 and this plug is inserted in the main plug 68 for connection with the passageway I2, being substituted for the drawings.

In Figure 2 I have illustrated the system as it is being prepared for the draining, cleaning and filling operations. The diaphragnrbacking plate member is illustrated in the non diaphragm supporting position. However, at this time this plate is threadedly operated to a position in which it supports the diaphragm I5 against movement bythe fluid and in a neutral position. In cleaning and filling the system the pump 85 is operated until a pressure of preferably between 25 and 50 pounds per square inch is exerted upon the surface of the fluid in the reservoir 82. The valve 9| is then adjusted to permit the fluid to flow. from the outlet pipe 88 to the line-92 and the passageway 41 of the pressure transfer cell. The check valve 4 5 in the pressure transfer cell passageway permits this fluid to flow through the orifices 42 for admission to the cell chamber 4|. The hydraulic fluid under pressure flows through the orifices 5J'and the passageway 5| of the pressure transfer cell to the capillary line 64, and the main plug .8. The fluid under pressureis permitted to flow thrombthesystem and to drain there-' from by flowing through the plug member99 and the line '98 to Fe fluid drain container 9'|. The flow of fluidunde'r pressure insuresthat the varicus lines and passageways of thesystem are in a non-clogged and clean condition; The flow of fluid is permitted to continue until the fluid drained from the system is free of bubbles to thus indicate that the fluid in the system is free from the presence of air. When the system has been thus checked and filled, the manually operated valve 9| of the fluid reservoir is closed and the fiow of fluid to the system is discontinued. The fluid is permitted to escape by continuing the draining operation until the pressure of the fluid remaining in the system has decreased to a desures occurring in the chambers 'I I4 and MI. In this position the end portion of the backing plate v .disc member I20 is supported against thecover phragm and locked in a position having the gasket member 23 in engagement with the casing member I6'of the pressure transfer cell. This diaphragm backing plate 20 is employed to support the diaphragm in a non-deflected position not only, whenthe system is being filled with the hydraulic fluid but also when it is desired to discontinue operation of the system, for example, upon disconnecting the pressure transfer cell i from the fuel or other lines or when the valve II is turned to the closed position.

In Figure 3 I have illustrated a modification and preferred embodiment of my fluid pressure transfer cell unit. In this embodiment the pressure transfer cell unit consists of a first casing member H6 and a second casing member I40. The diaphragm H5 is supported between the casing members and the. casing members are securely bolted or clamped together in any well known manner. The casing member H6 is so shaped that together with the diaphragm II5 it forms a chamber H4. Also, the casing member I40 is I so shaped that together with the diaphragm I I5 it forms the chamber I. A threaded passageway H3 is formed in one end of the casing member I I8 to provide for connecting the pressure transfer cell with the fluid fuel line or with a desired line containing fluid of variable fluid pressure. The threaded passageway I29 is also provided in the casing member H6 for the purpose of connecting either a fluid pressure actuated switch or a plug member thereto. The casing member I40 has formed therein a threaded passageway I5I and the orifices I50 which communicate with the passageway I5I and with the chamber I. A threaded passageway I53 is also formed in the-casing member I40 together with the orifices I42 extending between the passageway I43 and the chamber I4I. The passageway I43 contains a check valve consistingof a valve seat I44, a ball valve I45 and a valve biasing spring I46.

It will be apparent that the above described parts of'the preferred embodiment of my pressure transfer cell correspond to similar parts and function in a similar manner to the transfer cell illustrated and described in connection with Figures 1 and 2 of the drawings. A somewhat elastic and relatively thick diaphragm I I 5 of the cellunit is not supported in a relatively taut manner by the casing members but is of ansize having a somewhat greater cross-sectional area than the maximum cross-section area of chambers H4 or MI. The cell unit of Figure 3 is illustrated with the backin plate member I locked in the position in which it supports the diaphragm H5 in a neutral position and serves to prevent deflection of the diaphragm as a result of variable presmember I 40. The backing plate is accordingly illustrated in the position to which it would be locked for supporting the diaphragm during the a time when the hydraulic fluid fill is being added to the system for checking and installation purposes.

The backing plate member I20 is supported upon a threaded plunger member E21 and a gasket member I23 is also secured to this plunger member. In my preferred embodiment, the plunger member contains means for readily and automatically locking the plunger member in both the diaphragm-supporting position and in the diaphragm operating position. For thi purpose a first sleeve plug member 200 is supported in the casing member H6. The sleeve member 200 in turn supports a second sleeve member 20I which has formed internally therein a double cam surface consisting of a slot 202- and a, helical shaped end portion 203, as illustrated by the dotted lines. A pin member 204 mounted upon the plunger member I2I cooperates with the cam surfaces formed in the sleeve member 20I and as illustrated is in engagement with the camend surface 203 for locking and retaining the plunger member in the position in which the-backing plate I20 supports the diaphragm. The threaded plunger member I2! carries thereon a washer 2I5, a lock Washer 2l6, a nut 2H and the manual operating knob 2I8 having knurled or milled.

the plunger to withdraw the pin from the cam slot 202 for support on the outer end of the cam sleeve member 20I The head of the plunger I2I is thus positioned in the recess formed in casing member H6 and the gasket I23'is placed in firmcontact with the gasketseating portion 205 of the casing I I5. The washer 2I5 and the lock washer 2I6 together with the nut member 2II are then positioned on the threaded plunger to securely lock the washer 2I5-against the end surface of the plug and sleeve member 200.

It will be noted that in each of the modifications of the pressure transfer 'cellthe positioning of the diaphragm is varied in accordance with the varying fluid pressures. The diaphragm is sufficiently elastic or preferably of sufiicient size in addition to being relatively elastic that the positions assumed by it in transmitting the fuel or other pressure to the hydraulic fluid through-' out the entire operating range of the instrument will not require the application of an appreciable force in providing for the positioning and pos-'- sible stretching of .the elastic diaphragm. Accordingly, the diaphragm is either sufficiently elastic'or of sufilcient size that it does not of itself exert a force in opposition t the pressures exerted thereon by the fuel and hydraulic fluids.

The diaphragm is also of suflicient size and strength that should a break or leak occur in the hydraulic line the diaphragm is capable of assuming a position in which it is supported by the casing member without rupture and undue.

stretching. Thus, .should a leak or break, develop in the hydraulic line it-would result in the diaphragm being more or-less suddenly subjected casing member is designed to. provide this support and enable the diaphragm to withstand the force of large pressures for preventing any escape of fuel from the fuel line to the hydraulic line in which the leak or break occurred.

The system of my invention is automatically compensated for temperature changes throughout the wide range of temperatures in which the system is operated. For this purpose in each modification of the pressure transfer; cell the volume of both of the chambers formed by the casing members is such that the diaphragm will not be positioned against or supported by the casing members throughout the entire range of operation for the instruments associated in the hy-- draulic line regardless of the effects of tempera ture upon the fluids in the fuel and hydraulic lines. It is accordingly of importance that chain bers H and I in Figures 1 and 3, respectively contain. a suflic'ien't volume of hydraulic fluid that throughout the range of instrument operation fiuid will be contained in this chamber regardless v of external temperature conditions. Also, the chambers 4| and I of Figures 1 and 3,- respectively, are of suflicient size that when in operation the diaphragms are not deflected sufficiently to receive support by the casing members within the range of operation of the instruments and throughout the range of external temperatures in which the system is operated. v

In the system of myinvention it is unnecessary to separately fill thein'strument with fluid prior to connecting the instrument with the fluid actuating lines in an effort to prevent an unduly large volume of air from being entrapped therein and adversely affecting the instrument operation. 4

An important feature of my invention concerns the extremely small amount of attention that is required in the maintenance or servicing of my system and the relative freedom of any necessity with hydraulic fluid when the system has initially been installed and properly sealed.

The embodiments of my invention as illustrated and described may obviously be modified accordingly the invention is to be defined only by thescope of the appended claims.

I claim as my invention:

1. In a pressure transfer device comprising a in said supporting position, a plurality of passageways communicating with said first and sec- 0nd chambers, one of said passageways for supplying a transmission fluid under pressure to the second of said chambers being restricted to dampen pulsations.

. 3. In a pressure transfer device comprising a casing, a diaphragm mounted in'said casing for dividing said casing to form first and second chambers therein, a diaphragm backing member a movable inthe first of said chambers, means positioning said backing member to support, said diaphragmagainst deflection in response to the Jpress'ure exerted ther eon from the opposite side,

there being ledge-means on the casing adjacent a the said diaphragm, for providing an abutment means for said backing member in supporting position, passageways communicating with said first and second chambers, one of said passageways providing for the admission of a transmission cfluid under pressure to the secondof said chambers, -and another of said passageways providing for egress of the transmission said second chamber.

4. A pressure transfer device comprising .a cas-' ing, a diaphragm mounted in said casingfczr div viding said casing into flrstand second adjacent chambers, the cross sectional area of the first of said chambers'adjacent the plane of the diaphragm being larger than the cross sectional area of the second of the said chambers adjacent the 'plane of the diaphragm, whereby to form a ledge on the casing in the second of said chambers, a:

diaphragm backing member movable in the chamber having said larger cross sectional area, said backing member having a smaller cross sectional area than the maximum cross sectional area of the said larger chamber, and means for positioning said backing member to support said diaphragm against deflection in response to' pressure exerted thereon from the opposite side,- said "for cleaning, checking and refilling of the system casing, a diaphragm mounted in said casing for ledge providing an abutment for said backin member in said supporting position, said casing having passageways'giving access to and egress from'said chambers.

5. A pressure transfer device comprising a casing, a diaphragm mounted in said casing for diwithin the spirit and scope of my invention and 50 ding Said casing twoadjacent chain bers therein, a diaphragm backing member movable in one of said chambers, means positioning said backing member to support said diaphragm;

cent the diaphragm being provided with an abutment' for said backing member in said supportagainst deflection in response to pressur exerted thereon from the opposite side, there being ledge means'on the casing in the second of said chambers for providing-abutmentmean for said backing means in said supporting position, and passageways communicating 0nd chambers. v

2. In a pressure transfer device comprising a casing, a diaphragm mounted in said casing for dividing said easing into first and second chamwith said first and secbers, a diaphragm backingmember movable in said first chamber, means positioning said backing member to support said diaphragm against deflectionin response topressure exerted thereon from the opposite side, there being ledge means on the casing adjacent the diaphragm for proproviding an abutment for in said supportingposition,

.ing position and passages giving access to-and egress from said chambers. v

6. A pressure transfer device comprisinga; casing, a diaphragm mounted in said casing for dividing said casing toform two adjacent chain bers therein, the cross-sectional area of one of said chambers adjacent theplane cfthe diaphragm being larger thanthe cross-sectional area of the other of said chambers adjacent the plane of the diaphragm, whereby to form a ledge on the casing adjacent the diaphragm. a diaphragm -backing member movable in the chamber having said larger cross-sectional area, means for positioning said backing member to support said diaphragm against deflection in response to pressuretheopposite side, said ledge said backing member and there being pas-- exerted thereon from viding abutment means for'said backing means abutment for said backing member in said supporting position, and there being passages in said casing,giving access to and egress from said chambers.

8. A pressure transfer device comprising a casing, a diaphragm mounted in said casing for dividing said casing to form two adjacent chambers therein, a diaphragm backing member movable in one of said chambers, means positioning said backing member to support said diaphragm against deflection in response to pressure exerted thereon from the opposite side, said casing adjacent the diaphragm being provided with an abutment for said backing member in said supporting position and passageways giving access to and egress from one of said chambers, at least one of said passageways restrictively regulating the flow of fluid therethrough.

9. A pressure transfer device comprising 9. casing, a diaphragm mounted in said casing for dividing said casing to form two adjacent chamsages in said casing giving access to and egress from said chambers.

bers therein, a diaphragm backing member movable in one of said chambers, means positioning said backing member to support said diaphragm against deflection in response to pressure exerted thereon from the opposite side, said casing adjacent the diaphragm being provided with an abutment for said backing member in said supporting position, and passageways giving access to and egress from said two adjacent chambers, at least one of said passageways comprising a plurality of orifices adapted to restrictiveiy regulate the flow of fluidtherethrough to prevent sudden application of abnormal pressure on the diaphragm upon the occurrence of abnormal differences between the pressures of the fluid in said chambers.

10. A pressure transfer device comprising a casing, a diaphragm mounted in said casing for dividing said casing to form two adjacent chambers therein, a diaphragm backing member movable in one of said chambers, means positioning said backing member to support said diaphragm against deflection in response to pressure exerted thereon from the opposite side, said casing being provided with an abutment for said backing member in'said supporting position and passageways giving access to and egress from said chambers, one of said passageways including a check valve allowing fluid entry into one of said chambers and preventing fluid egress from said chamber and also including means external to said chamber and outwardly from said valve for removably connecting a fluid supply member to supply fluid through said valve.

ALBERT E. BAAK, 

